1. Field of the Invention
The present invention relates to an improved rotor structure of a spindle motor intended for an optical disk such as a CD-ROM.
2. Description of the Prior Art
In response to a demand for increase in the motor rotational speed attendant on the recent high-speed equipment, the endeavor to enhance the motor performances has almost reached its limit and one of the remaining problems lies in removing any dead space from the motor, that is, effective utilization of the motor space. By the way, the conventional spindle motor for an optical disk comprises a turntable, a rotor yoke and a shaft which are separate components, with the turntable and the rotor yoke being assembled together by caulking, and with the turntable and the shaft being assembled together by press fitting. Such an example is shown FIG. 7.
FIG. 7 is a sectional view of such a conventional spindle motor.
As is apparent from FIG. 7, at the center of a turntable 12 made of a metal such as brass, a holder 41 is press fitted onto a shaft 15. The holder 41 adhesively holds a chucking magnet 10 for attracting an optical disk 1. On the outer periphery of the holder 41, a guide 42 is retained by a spring 43 in an axially displaceable manner. The guide 42 serves to guide the optical disk 1 toward the center of the turntable 12.
A rubber ring sheet 11 is adhered to the outer periphery of the turntable 12. The rubber ring sheet 11 serves as a slip resistant material for the optical disk 1. A rotor yoke 13 is joined by caulking to the underside of the turntable 12 in such a manner that the rotor yoke 13 is coaxial with the turntable 12. It is natural that a magnetized rotor magnet 14 be adhered to the rotor yoke 13. Also, as is apparent from FIG. 7, a gap is defined between the turntable 12 and the rotor yoke 13 to provide an uneven contour.
The spindle motor for an optical disk needs a high precision, and hence each of the components used therein also requires a high precision. To this end, each component needs a high rigidity. To enhance the rigidity, the dimensions of the components are enlarged in a degree. As a result, a space available for the motor to provide a magnetic circuit is reduced, resulting in an inefficient utilization of the space. Each of the components needs to be manufactured at a high precision, so that it is impossible to reduce the production cost, leading to a high price. Thus, the conventional spindle motor has failed in not only obtaining desired motor performances but also in complying with the demand for a reduction in cost.
The present invention was conceived in view of the above circumstances. It is therefore an object of the present invention to provide a rotor structure capable of achieving an increase in the power output, an improvement in the productivity and a reduction in the production cost, without any need to change the external dimensions of the motor.
Measures to increase the power output without changing the dimensions of the motor include eliminating the gaps which have been formed on the underside of the turntable and on the top of the rotor yoke and reducing the unevenness on the outer side surface to extend the height of the rotor yoke by the distance of the gaps and to lengthen the rotor magnet to enhance the capability of the magnet, while simultaneously increasing the number of magnetic plates for the stator yokes inside the rotor yoke to thereby enhance the capability of the magnetic circuit of the stator corresponding to the magnet, thus achieving a high power output.
Furthermore, the material of the turntable can be resin in place of the metal which has hitherto been used, to thereby reduce the material cost. The rotor yoke and the shaft are integrated with the turntable by insert molding. The chucking magnet, the rotor yoke and the shaft may be integrated with the turntable by insert molding, to provide a high-performance rotor at a lower cost and having a high productivity as well as allowing a reduction in size of the motor.
The rotor yoke and the shaft are integrally insert molded into any one or a combination of the turntable, the rotor magnet and the chucking magnet which may also be formed from a rare plastic magnet material. Moreover, the chucking magnet may be provided with a back yoke to achieve an improvement in the chucking properties, thus realizing a high-speed and low-cost spindle motor.